Improved resistance to softening and high electrical conductivity of copper and copper base alloys is of considerable interest in electronics applications. This is due to the fact that short time exposure to fairly high heat such as that used in soldering and spot welding operations, used extensively in such applications, causes loss of strength of cold worked material utilized as semiconductor lead frames and heat sinks. The alloys which have most commonly been utilized for such applications have been the silver-bearing, tough-pitch and oxygen-free copper base alloys containing up to 25 troy ounces of silver per avoirdupois ton of alloy. Other alloys which have been suggested for such applications include a copper base alloy containing between 0.02 and 1.5% by weight niobium, either with or without an aluminum addition ranging between 0.1 and 1.0% by weight such as that found in U.S. Pat. No. 2,422,752. Alloy 155 (Copper Development Association designation) is reported to exhibit high electrical conductivity (90% IACS in the annealed temper) and high resistance to softening through the addition of between 8 and 30 ounces of silver per ton of alloy in conjunction with 0.04 to 0.08% by weight phosphorus and 0.01 to 0.12% by weight magnesium.
The combination of magnesium and zirconium has been proposed as an addition to copper in U.S. Pat. No. 3,392,016 in order to improve the softening resistance of copper which is subjected to high temperature conditions such as soldering. This patent compares the magnesium-zirconium copper with such alloys as copper-zirconium-phosphorus alloys. There is no indication in the patent that niobium may be added to such an alloy.